The use of aqueous copolymer dispersions as binders for bonding and coating fiber structures such as woven fabrics, nonwovens and waddings of textile fiber or textile yarns is known. Copolymer dispersions of (meth)acrylate or vinyl ester copolymers which comprise self-crosslinking comonomer units with N-methylol or N-methylol ether functions to improve their strength are often used here. Up to 10% by weight of N-methylol(meth)acrylamide (NMA or NMMA) are usually copolymerized. Disadvantages of these binders are the release of formaldehyde due to cleavage of the N-methylol function and the low resistance to solvents of the materials bonded or coated with them. Improvement of the resistance to solvents by incorporation of precrosslinking, poly-ethylenically unsaturated comonomer units is known. However, this measure often leads to problems in the preparation of the copolymer dispersions.
Thermally self-crosslinking copolymers which comprise 2 to 10% by weight of N-methylol(meth)acrylamide or the N-methylol ether thereof are known from DE-A 2512589 (U.S. Pat. No. 4,044,197). The copolymer dispersions are prepared in the presence of any desired anionic, cationic or nonionic emulsifiers, anionic and nonionic emulsifiers being preferred. A disadvantage is that, although in the case of the N-methylolacrylamide-containing copolymers used therein the heat-treated copolymer films show a good resistance to solvents, the nonwovens bonded with them do not.
EP-B 205862 relates to textile binders based on vinyl acetate/ethylene copolymers which comprise 1 to 5% by weight of N-methylol(meth)acrylamide units or ethers thereof. To improve the wet strength if a copolymer binder of low NMA content is used, the additional use of melamine-formaldehyde resins is proposed. The polymerization is carried out in the presence of anionic or nonionic emulsifiers.
The doctrine of EP-A 261378 is to improve the heat stability of fiber mats bonded with N-methylol functional styrene/acrylate copolymers by employing as binders those copolymers in which the N-methylol functions are completely or partly etherified. The polymerization can take place in the presence of any desired nonionic or anionic emulsifiers.
WO-A 92/08835 describes textile binders based on vinyl acetate/ethylene copolymer emulsions which comprise exclusively N-(n-butoxymethyl)acrylamide units instead of N-methylol(meth)acrylamide units to reduce the release of formaldehyde. For the preparation according to the emulsion polymerization process, the usual ionic or nonionic emulsifiers can be used.
EP-A 86889 (AU-A 8310718) relates to a process for the preparation of a textile coating composition which shows no white swelling and no white fracture under the action of water. The coating composition comprises an aqueous copolymer emulsion which is obtained by emulsion copolymerization of (meth)acrylates with N-methylol(meth)acrylamide, the N-methylol(meth)acrylamides being etherified to the extent of at least 20 mol % with an alcohol and the emulsion polymerization being carried out in the presence of a mixture of fatty alcohol having 10 to 20 C atoms and fatty alcohol adducts of alkylene oxides or alkylphenols.
In DE-A 4432945 (WO-A 96/08597) it is proposed, for improving the solvent resistance, to employ textile binders with a mixture of N-methylol-functional comonomer units and N-methylol ether-functional comonomer units. By this means a marked improvement in solvent resistance is obtained, although this is still not satisfactory for certain applications, especially in the case of soft textile binders--for example, ethylene-vinyl acetate copolymers of high ethylene content.